The United States will signal its resolve to protect its NATO allies near Russia's borders on Tuesday with the start of the first joint military training exercises in the region since the Kremlin intervened in Ukraine.

In the Black Sea, across the water from the Crimean Peninsula where Russian military groups have seized control from Ukrainian authorities, a US navy destroyer will take part in manoeuvres with Romanian and Bulgarian warships.

To the north in Poland, US fighter jets are arriving at the central Lask air base to take part in joint exercises, with Poland's president expected to review the manoeuvres.

The United States stressed that both training drills were planned before the Ukraine crisis, but they are also a signal of support for NATO members nervous that if Russia is prepared to intervene in Ukraine, they could be next.

The exercises underline that it is Washington which has so far taken the lead in the international response to Russia's actions in Ukraine, while the European Union, hampered by the need for consensus among its members, has been less bold.